Called an overshirt, because it's a heavyweight button down that can be worn alone... or you know, over a shirt. Wear it as a shacket over a tee, or by itself. Ya can't go wrong.
We're using the same fabric we use for our Corbets, but we made it a little thicker for this guy, so you can wear it as a jacket-type thing. We also gave it a different color inside, so you can show a little contrast color depending on how you roll (... up your sleeves).